how do i get my battery capacity to go back up?

Similar to living beings, once a battery undergoes the aging process and degrades, it cannot be reversed.

Protect & Prolong the Life of your iPhone's Battery:

1. About the battery usage on your iPhone, iPad, and iPod touch ...
2. Batteries - Maximising Performance - Apple (IN)
3. iPhone Battery and Performance

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To prolong the life of your iPhone battery, you can follow these tips and best practices:

To prolong the life of your iPhone battery, you can follow these tips and best practices:

1. Optimize Battery Charging: Enable the "Optimized Battery Charging" feature on your iPhone. It helps reduce the wear on the battery by slowing down the battery aging process. You can find this option in Settings > Battery > Battery Health.
2. Avoid Extreme Temperatures: Extreme temperatures, both hot and cold, can negatively impact your battery life. Avoid exposing your iPhone to excessive heat or cold, such as leaving it in direct sunlight or in a freezing car.
3. Use Original Chargers and Cables: Always use Apple's original chargers and cables or certified third-party accessories. Low-quality chargers or cables can damage the battery and reduce its lifespan.
4. Avoid Draining the Battery to Zero: Charge it whenever the charge becomes lower than 20%
5. Optimize Display Settings: Adjust your display settings to optimize battery life. Lower the screen brightness, enable auto-brightness, and use shorter screen timeout durations.
6. Minimize Background App Refresh: Limit the number of apps allowed to refresh in the background. Go to Settings > General > Background App Refresh and disable it for apps that don't require real-time updates.
7. Disable Push Email: Push email notifications can drain your battery quickly. Instead, set your email accounts to fetch data manually or at longer intervals. You can change this setting in Settings > Mail > Accounts > Fetch New Data.
8. Disable Unnecessary Notifications: Reduce the number of unnecessary notifications you receive. Go to Settings > Notifications and customize which apps can send you notifications.
9. Limit Location Services: Some apps use GPS and location services in the background, which can drain your battery. Go to Settings > Privacy > Location Services and disable location access for apps that don't require it.
10. Update iOS: Keep your iPhone's operating system up to date. Apple regularly releases updates that can include optimizations and improvements for battery life.
11. Limit Background App Activity: Close or force quit apps that are running in the background but are not needed. Double-press the home button (or swipe up from the bottom on iPhone X or later) and swipe away the unnecessary apps.
12. Enable Low Power Mode: When your battery is running low, enable Low Power Mode in Settings > Battery. It reduces power consumption by disabling non-essential features.
13. Avoid Battery Drain during Storage: If you need to store your iPhone for an extended period, make sure to charge it to around 50% first. This helps prevent the battery from draining completely, which can be harmful.
14. Disable Dynamic Backgrounds and Motion Effects: Dynamic backgrounds and motion effects use additional processing power and can impact battery life. Use a static wallpaper and disable parallax motion effects in Settings > Accessibility > Motion > Reduce Motion.
15. Limit Widgets: Widgets on the Today View can consume battery life. Remove or limit the number of widgets displayed by swiping right on the home screen, scrolling to the bottom, and tapping Edit.
16. Adjust Auto-Lock Time: Shorten the auto-lock time on your iPhone. Go to Settings > Display & Brightness > Auto-Lock, and select a shorter time interval to turn off the screen more quickly when not in use.
17. Use Wi-Fi Instead of Cellular Data: When possible, connect to Wi-Fi networks instead of relying on cellular data. Using Wi-Fi consumes less power than using cellular data.
18. Enable Airplane Mode in Low or No Coverage Areas: When you're in an area with low or no cellular coverage, enabling Airplane Mode can prevent your iPhone from constantly searching for a signal and draining the battery.
19. Disable Background App Refresh for Cellular Data: If you have limited data plans, consider disabling Background App Refresh for cellular data to reduce data usage and preserve battery life. You can find this option in Settings > General > Background App Refresh.

By following these tips, you can help prolong the battery life of your iPhone and maintain its overall performance over time.